Water soluble epoxy ester copolymers for interior can use

ABSTRACT

Epoxy ester copolymer dispersible in water with the aid of an amine, which may be ammonia, is provided by esterifying a polyepoxide having a 1,2-epoxy equivalency in excess of 1.0 and a molecular weight of from 350 to 8000 with at least 0.5% of the weight of the copolymer of a monoester of a saturated monohydric alcohol with a monoethylenically unsaturated dicarboxylic acid which resists homopolymerization. This polyepoxide ester is copolymerized with from 15% to 70% of monoethylenic monomers, based on the weight of the copolymer, these monoethylenic monomers including carboxyl functional monomer providing an acid number of from 20-150 in the copolymer.

This is a division, of application Ser. No. 153,429, filed 5/27/80, U.S.Pat. No. 4,294,737, which, in turn, is a continuation-in-part of Ser.No. 108,283, filed 12/28/79, now abandoned.

This invention is an improvement over the water soluble epoxy estercopolymers disclosed in our prior applications Ser. No. 18,887, filedMar. 9, 1979, which is a continuation-in-part of Ser. No. 885,036, filedMar. 9, 1978, and now abandoned.

TECHNICAL FIELD

This invention relates to water soluble epoxy ester copolymers which areparticularly adapted to interior can use where good resistance toextraction by hot water and good odor and flavor characteristics areimportant, especially for beer and beverage packaging. Other usesincluding exterior can use are also contemplated.

BACKGROUND ART

Water solution coating compositions have been employed for diversepurposes, but it has been difficult to obtain the good resistance toextraction by hot water and good odor and flavor characteristics whichare important to enable application of the coatings to sanitary cans.

In our applications Ser. Nos. 885,036 and 18,887, a relatively lowmolecular weight polyepoxide, such as a diglycidyl ether of a bisphenol,is esterified with an at least approximately stoichiometric proportionof monocarboxylic acid selected from benzoic acid, a C₁ -C₈alkyl-substituted benzoic acid, or a C₆ -C₁₀ alkanoic acid to produce anester derivative substantially free of epoxy functionality. Theresulting hydroxy functional epoxy ester is then polyesterified with asmall amount of monoethylenic dicarboxylic acid which resistshomopolymerization, such as fumaric acid, and this unsaturated polyesteris then copolymerized with monoethylenic monomers includingcarboxyl-functional monomer to provide a copolymer which is dispersed inwater with the aid of an amine.

It is also known to copolymerize monoethylenic monomers includingcarboxyl-functional monomer in the presence of a polyepoxide, but thisleaves most of the epoxide groups unreacted and much of the copolymerformed remains unassociated with the polyepoxide.

These systems are each inadequate in certain respects, particularlybecause organic amines are needed for good solubility and stability inwater. It is desired to use ammonia because organic amines introduce thepossibility of nitrosamine formation, and also because ammonia is moreeconomical and its vapors are less troublesome.

DISCLOSURE OF INVENTION

In this invention, a polyepoxide of somewhat higher molecular weightthan used in Ser. Nos. 885,034 and 18,887 is esterified with at leastabout 1% by weight, based on the total weight of the final epoxy estercopolymer, of a monoester of a saturated monohydric alcohol with amonoethylenically unsaturated dicarboxylic acid which resistshomopolymerization, such as monobutyl maleate, to produce an unsaturatedester derivative which may or may not contain residual epoxyfunctionality. This unsaturated ester is then copolymerized with from15% to 70% of monoethylenic monomers, based on the weight of thecopolymer, to provide a copolymer product. These monomers includemonoethylenic carboxylic acid, such as methacrylic acid or fumaric acid,to provide an acid number of from 20-150, preferably 50-120 in the finalcopolymer so that amine (preferably ammonia) and water can be added toprovide a water dispersion which is either a solution or a colloidaldispersion. Reactive monomers, such as hydroxyethyl acrylate orN-methylol acrylamide (or an ether thereof such as the butyl ether) maybe used. Alternatively, an aminoplast, such as hexamethoxy methylmelamine, or a water soluble or dispersible phenoplast, or a mixturethereof, may be used for cure. In preferred practice, from 2-30%, basedon the total weight of resin, of hexamethoxy methyl melamine monomer ora low molecular weight polymer thereof is used to provide solventresistance properties in the cured coating. Union carbide productResimene X 2735 and American Cyanamid product Cymel 370 will illustratecommercial products which may be used.

While very little maleate is needed in this invention, it isindispensible. In the absence of the maleate component, the addition ofwater and ammonia yielded a mixture which separated on standing. In thesame system, the use of the maleate in an amount of 1.7% of the weightof the copolymer provides a stable aqueous dispersion.

The polyepoxides preferably have a 1,2-epoxy equivalency of about 1.4 toabout 2.0, but it is only necessary that the epoxy equivalence be morethan 1.0. The best properties are obtained using diglycidyl ethers of abisphenol, such as bisphenol A. The molecular weight of thepolyepoxides, which may be provided by the use of mixtures, is from 350to 8000, preferably 1500 to 5000.

The monoesters of a saturated monohydric alcohol with amonoethylenically unsaturated dicarboxylic acid which resistshomopolymerization can vary with the alcohol selected and the acid whichis chosen. C₁ -C₁₈ alkanols, preferably C₂ -C₈ alkanols are preferred.It is not desired to have the alcohol contain significant unsaturationbecause this provides too many unsaturated groups. Thus, allyl alcoholleads to a tendency to gel. The preferred alcohol is a butanol, such asn-butanol or isobutanol, but ethanol, propanol, 2-ethoxy ethanol,2-ethylhexanol, and the like, are all useful, alone or in combination.

Maleic acid, fumaric acid and itaconic acids will illustrate theunsaturated dicarboxylic acids which can be used. It is preferred toform the monoester from the acid in its anhydride form, but this is abackground feature herein, and is itself well known.

The maleic half esters are especially preferred and introduceconsiderable economy into the products of this invention.

While ammonium hydroxide is preferred, organic amines, such as dimethylethanol amine, are also useful, and both are embraced by the language"volatile amine". While ammonium hydroxide provides important benefits,as has been noted, there are advantages, such as the capacity to depositthicker coatings, which favor the use of amines in some circumstances.

The esterification reaction is wholly conventional, simple heating to ahot melt, optionally in the presence of a trace of amine catalyst, beingall that is needed. The maleic half ester or other acid is used in anamount of at least about 0.5%, but preferably in an amount of at least1.0% based on the final copolymer. Based on stoichiometry, it ispreferred to use at least 50%, based on the epoxide functionalityavailable for esterification. The esterification reaction is continuedto substantial completion, though some unreacted epoxy or acidfunctionality is not harmful. At least 0.5%, preferably at least 1.0%maleate should be reacted to form an ester with the polyepoxide.

The epoxy ester which is provided contains polymerizable unsaturation,and it is copolymerized with monoethylenic monomers, the bulk of which(at least about %0% by weight) are nonreactive. This means that, asidefrom their polymerizable unsaturation, they do not react under theconditions of polymerization and use which are contemplated. A similarstatement is that there are no functional groups except thepolymerizable ethylenic group. Styrene and vinyl toluene areparticularly contemplated, though methyl methacrylate, methyl acrylate,ethyl acrylate, acrylonitrile and vinyl acetate will further illustratethe useful materials. Styrene and vinyl toluene are especially importantbecause they copolymerize well with the unsaturated monoesters used foresterification.

Other reactive monoethylenic monomers may be included in an amount up toabout 20% of the total polymerizable monomers. These are illustrated byhydroxy monomers, such as 2-hydroxyethyl acrylate, amide monomers, suchas acrylamide, N-methylol functional monomers, such as N-methylolacrylamide or ethers thereof, like the butyl ether.

The copolymerization is itself conventional, being carried out inorganic solvent solution using a free radical generating polymerizationcatalyst. These are well known and are illustrated in the examples.

The aminoplast and phenoplast resins which may be used for cure are alsowell known, and have been illustrated heretofore. This class of watersoluble and water dispersible curing agents for curing hydroxyfunctional resins is a matter of common knowledge in the art. They maybe used in an amount up to about 40% of total resin solids, though theiruse is desirably minimized.

The resulting aqueous solutions cure to provide films characterized bysuperior resistance to extraction and they resist absorbing odor andflavor components of the foods and beverages which are packaged. Theycan be applied to any metal can interior, such as aluminum, steel andtin-plated steel. Spray application and cure by baking at 400° F. for 3minutes are particularly contemplated. Films of about 0.2-0.3 mil areusually formed. Good adhesion is obtained on all of these surfaces.

BEST MODE FOR CARRYING OUT THE INVENTION

The invention is illustrated in the following examples of preferredoperation, all parts herein being by weight except where otherwisenoted.

EXAMPLE 1 (FORMATION OF MONOBUTYL MALEATE)

45 parts of n-butanol and 49 parts of maleic anhydride are charged to areactor equipped with a reflux condenser and the mixture is heated to110° C. and maintained at that temperature for 2 hours during which timethe reaction went to completion.

EXAMPLE 2

The product of Example 1 is diluted with 330 parts of n-butanol and 330parts of 2-butoxy ethanol and then 1000 parts of a diglycidyl ether ofbisphenol A having a molecular weight of about 3500 is added slowly over30 minutes to the solution which is maintained at 110° C.-120° C. Thecommercial epoxy resin Epon 1007 may be used. The epoxy resin dissolvedin the hot solution containing the monobutyl maleate.

4 parts of alkaline catalyst (sodium carbonate) are added to the hotsolution and the temperature adjusted to 120° C.-125° C. and theesterification reaction proceeds. The reaction is allowed to continueuntil the acid value falls below 3 to produce an unsaturated epoxy estersolution.

EXAMPLE 3

A monomer premix is made by mixing together 150 parts of styrene, 100parts of methacrylic acid and 35 parts of cumene hydroperoxide. Thispremix is slowly added to the hot unsaturated epoxy ester solution ofExample 2 at 120° C. over a 21/2 hour period. After monomer addition hasbeen completed, the copolymerization reaction mixture is held at 120° C.for 1 hour and 10 parts of cumene hydroperoxide are then added on twooccasions with a 1 hour hold each time to insure complete conversion ofmonomer to copolymer.

EXAMPLE 4

The copolymer solution of Example 3 is cooled to 80° C. and then 160parts of a 28% ammonium hydroxide water solution are added withagitation over a 20 minute period. 2200 parts of deionized water arethan added over 30 minutes with agitation, and the dispersion product iscooled to 35° C. and strained.

The product is a stable, milky aqueous dispersion containing 32% resinsolids with an acid value of 50.

EXAMPLE 5

Hexamethoxymethyl melamine in an amount of 15% by weight of the resinsolids in the aqueous dispersion product of Example 4 is placed in acontainer together with enough n-butanol tl provide a final weight ratioof water to organic solvent of 80:20. The aqueous dispersion is thenslowly added with agitation. The final product contains about 22% ofresin solids and provides a spray solution which deposits a clearcoating.

The sprayed on coating is baked at 400° F. for 3 minutes to provide afinal coating of 15 mg/4 sq. in. which exhibited good adhesion andpossessed good resistance to pasteurization. The cured film passed 100double rubs with a methyl ethyl ketone saturated cloth. No objectionableflavor or odor was produced.

EXAMPLE 6

540 grams of Dow product DER-333 (a precatalyzed diglycidyl ether ofbisphenol A having an epoxide equivalent weight of 190) are charged to areactor together with 155 grams of 2-butoxy ethanol. To this is added338 grams of bisphenol A and the mixture is heated to 170° C. and heldfor 2 hours. The product is an epoxy functional polyepoxide of increasedmolecular weight (about the same as Epon 1007).

There is then added 20 grams of monobutyl maleate prepared as in Example1 and the mixture is held for 2 hours at 170° C. to provide an acidnumber of less than 1. The product is cooled, 350 grams of n-butanol areadded, and then the system is reheated at 120° C.

There is separately prepared a premix of 183 grams of methacrylic acid,96 grams of styrene and 3 grams of ethyl acrylate in 80 grams of2-butoxy ethanol containing 19 grams of benzoyl peroxide. This premix isslowly added to the reactor over a 2 hour period at 120° C. The mixtureis held for 1 hour and then 8 grams of cumene hydroperoxide are addedand the mixture is held for another 11/2 hours to complete theconversion of monomers to copolymer.

The copolymer solution is then cooled and 80 grams of 2-butoxy ethanoland 120 grams of n-butanol are added at 105° C. The solution productcontains 60.8% solids and has a Gardner viscosity of Z7-Z8. The acidvalue of the solids is 93.3.

EXAMPLE 7

1000 parts of the solution of Example 6 has added thereto 61.1 parts ofdimethyl ethanol amine and then 19.4 parts of hexamethoxy methylmelamine are added. 1000 parts of deionized water are then added withagitation to get a uniform solution. This solution is diluted with 700parts of deionized water to provide a coating composition adapted forspray application and which contains 21% solids and has a #4 Ford cupviscosity at room temperature of 32 seconds.

This solution is used to provide an aqueous spray for can interiors(two-piece aluminum cans). The coatings are cured at 400° F. for 3minutes to provide cured coatings weighing 15 mg/4 sq. in. Thesecoatings exhibit excellent beer and water pasteurization resistance andexcellent adhesion to the substrate. The cured film passed 10-15 doublerubs with a methyl ethyl ketone-saturated cloth. No objectionable flavoror odor was produced.

This example was then repeated only the dimethyl ethanol amine isreplaced with a corresponding equivalent proportion of ammoniumhydroxide. The same excellent results are obtained. The aqueouscompositions are excellently stable regardless of the choice of organicamine or ammonia.

If the monobutyl maleate in Example 6 is omitted, the ammoniumhydroxide-containing aqueous composition separated into three distinctlayers after standing for 2 weeks at room temperature.

A commercial acrylic copolymer formed by polymerization in the presenceof epoxy resin and which has much the same composition as used inExample 6 except there is no esterification with monobutyl maleate, wascompared to the product of example 7. In making this comparison,dimethyl formamide was added to the aqueous compositions being comparedin order to solubilize the dispersed resin solids. This is done to allowthe water and solubilizing amine to be removed which enable furthertests to be performed. As expected, the commercial composition formed aclear solution upon the addition of a small quantity of dimethylformamide. Surprisingly, the aqueous composition of Example 7 yielded acloudy dispersion, and the dispersed particles did not pass through a 5micron filter. Thus, the two products are quite different since one insalt form dissolves in a strong solvent and the other in the same formdid not. The basis for this difference is not now apparent.

What is claimed is:
 1. Epoxy ester copolymer dispersible in water withthe aid of an amine comprising a polyepoxide having a 1,2-epoxyequivalency in excess of 1.0 and a molecular weight of from 350 to 8000esterified with at least about 0.5% of a monoester of a saturatedmonohydric alcohol with a monoethylenically unsaturated dicarboxylicacid which resists homopolymerization to produce a polyepoxide ester,said polyepoxide ester being copolymerized with from 15% to 70% ofmonoethylenic monomers including carboxy functional monomer providing anacid number of from 20-150 in the copolymer, all of said proportionsbeing based on the final copolymer of said monomers with saidpolyepoxide ester.
 2. Epoxy ester copolymer as recited in claim 1 inwhich said polyepoxide is a diglycidyl ether of a bisphenol having a1,2-epoxy equivalency of from 1.4 to 2.0.
 3. Epoxy ester copolymer asrecited in claims 1 or 2 in which said polyepoxide has an averagemolecular weight of from 1500 to
 5000. 4. Epoxy ester copolymer asrecited in claim 1 in which said monoester is the reaction product of C₂-C₈ alcohol with maleic anhydride.
 5. Epoxy ester copolymer as recitedin claim 4 in which said monoester is monobutyl maleate.
 6. Epoxy estercopolymer as recited in claim 1 in which said monoester is used in anamount of at least 50% of the stoichiometric amount with respect to theepoxy functionality in said polyepoxide.
 7. Epoxy ester copolymer asrecited in claim 1 in which said monoester is used in an amount of atleast 1% of the copolymer and at least 50% of said monomers arenonreactive.
 8. Epoxy ester copolymer as recited in claim 7 in whichsaid nonreactive monomers consist of styrene and vinyl toluene.
 9. Epoxyester copolymer as recited in claim 7 in which the functionality of anynonacidic reactive monomer is selected from the group consisting ofhydroxy, amide and N-methylol amide.
 10. Epoxy ester copolymer asrecited in claim 1 in which said copolymer has an acid number of from 50to
 120. 11. Epoxy ester copolymer as recited in claim 3 in which saidpolyepoxide is esterified with said monoester to be substantially freeof epoxy functionality.